cylinder head inner o-ring keeps blowing

dx787
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dx787
Edited Date/Time 8/1/2017 7:45pm
I have an 01 rm125. Low sided around a turn, fired it up and got bike back to truck, not far, then wouldnt fire. Popped off head and the inner o ring blew which is what im assuming caused the coolant to flood the cylinder. Took the exhaust off and poured out maybe a half of a bottle of water worth. and tried to dry and blow out as much water as possible. Also drained the oil. The oil looked perfect and not one bit of water was inside. There still sounds like there maybe some water when i try to turn it over. With the exhaust off and plug out, I tried to kick it over a few times to clear remaining water out but still seems pretty wet. The inner and outer head o rings have been replaced and not losing any coolant or see any bubbles when I do kick it over now. Do i let it dry out or should i pull the jug off? Also since the two times ive rode since ive bought the bike, ive blown the inner o ring on the head both times. I torqued it to spec at 18 lbs/ft in cross pattern. This time i just put a new head since the original looked pretty worn (little dings and scuffed interior side). My other question is why do they keep blowing out? Thank for any help
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Paw Paw 271
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Paw Paw 271 9/17/2015 2:15pm
9/17/2015 2:15pm
Sounds like too much heat is being generated and thus the o ring fails. This can be from too lean jetting, air leak, wrong combination of head and piston causing preignition. That would explain the pits in the old head.
Are you sure you have the correct head?
The correct piston?
I have seen this issue come up when an owner puts a domed piston in an engine with a head designed for a flat top piston. I see this a lot in Suzuki 125's.

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dx787
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dx787 9/17/2015 2:33pm
9/17/2015 2:33pm Edited Date/Time 8/1/2017 7:47pm
I bought an oem head but just installed it and havent had it running with it on. The old head looks identical so im assuming its the same. The guy i bought it from said it had a new piston (oem size not bored) with maybe a few hours on it. So maybe the head was from prior piston issues. Looks like it had a slight dome not flat top, and one of our local shops did the install. I know words are cheap, but i do believe him. The piston and cylinder walls look pretty clean. Before the last ride i put a new plug, prohonda 80w oil, air filter, and topped off coolant. The plug has a good amount of carbon and no white so by the looks of that alone seems ok. It felt and sounded great when running. And was reading about 150+ on compression test before the ride. It all started when i layed it down and rode it for maybe 30 seconds after. Probably gonna pull carb and drain it incase water filled the intake. Could there be water trapped somewhere under the piston that wont come out of the drain plug? Just seems too wet when i turn it over. Sucks i drained brand new oil when there was no water even in there. Should i pull jug or let it dry out for a day or two? thanks
Jakes Dad
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Jakes Dad 9/17/2015 5:45pm
9/17/2015 5:45pm
Check the squish, you want it tight to prevent the heat getting to outside edges of the cylinder. Jake's 125's I ran .028 to .030 at a 55% band width.
SLOWTIME
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SLOWTIME 9/17/2015 6:32pm
9/17/2015 6:32pm
Draining the oil has no effect on the water around your crank.

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Paw Paw 271
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Paw Paw 271 9/17/2015 7:21pm
9/17/2015 7:21pm
Yes there is a cavity where the crank is located in the cases. If you had water in the cylinder and on piston, then you for sure have water down in the crank cavity.
Pull the fuel tank & spark plug.
Turn the bike upside down so the spark plug hole is pointed to the ground and turn the engine over several times. You can do this by putting the engine in gear and rotating the rear wheel several revolutions. Then take compressed air and blow into the spark plug hole.
Now put the bike up right and put the fuel tank and spark plug back on the bike and try to start it. You need to run it at this point so you can get lubrication from the fuel mix to the crank bearings, rod bearings and etc so they will not rust.

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dx787
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dx787 9/17/2015 7:39pm
9/17/2015 7:39pm Edited Date/Time 9/17/2015 7:42pm
Gonna flip the bike to clear remainder of water and see if she'll fire. As far as squish, what should i use, solder? Do I pop hear off lay solder across top of piston, install head, crank a few times and measure with micrometer? If squish is too much does head need to be milled? How do I check band width? Will carb be filled with water as well or is that a waste like draining the oil? Thanks for all the help so far yall are awesome
harescrambled 9/17/2015 11:27pm
9/17/2015 11:27pm
dx787 wrote:
Gonna flip the bike to clear remainder of water and see if she'll fire. As far as squish, what should i use, solder? Do I pop...
Gonna flip the bike to clear remainder of water and see if she'll fire. As far as squish, what should i use, solder? Do I pop hear off lay solder across top of piston, install head, crank a few times and measure with micrometer? If squish is too much does head need to be milled? How do I check band width? Will carb be filled with water as well or is that a waste like draining the oil? Thanks for all the help so far yall are awesome
If all that happened is you blew the inner O-ring, it's not necessary to drain the carb. Blown head O-rings won't load the carb up with water. Besides which, if you sank the bike in water and did need to drain the carb, you can either unscrew the carb drain, or remove the nut that sits under the main jet...either one would drain any water out of the float bowl. I'm on a bender right now, and can't remember which one would be required for your bike.
dx787
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dx787 10/7/2015 5:22pm
10/7/2015 5:22pm
Drained all the water then blew it out with compressor. Had to take off jug to drain all the water. Put new base gasket, new o rings on head. Cylinder walls looked great, piston looked great. Torqued everything down to spec. Did a compression test and still only pulling 90 psi max after 10-15 kicks. 30 psi after 1st, 60 psi after 4th kick etc. Where could I be losing compression? I doubt the the cylinder or piston are the culprit especially since it ran great until the jug filled up with water. The ring was facing towards the intake so im assuming its not aftermarket.
colintrax
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colintrax 10/7/2015 9:23pm
10/7/2015 9:23pm
How well did you check the piston and walls? My head o ring let go recently, jug needs to be replated and the piston was scoured. I doubt yours survived much better
dx787
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dx787 10/8/2015 3:44am
10/8/2015 3:44am
The cylinder walls looked brand new. No scratches. The only thing was on top of piston along outer edge was a tiny looking "burn" but couldn't feel any defect. Ill most likely pull it back apart to check ring gap and take a few pictures and try and upload them.
Bruce372
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Bruce372 10/8/2015 7:42am
10/8/2015 7:42am
Take a picture of the top of the cylinder, it might need to be repaired.

Modern ethanol pump fuels detonate real bad in older 2 strokes, and the very top of the cylinder gets burnt away and then the o-ring gets burnt away.

Look for pitting at the very top of the cylinder plating.
dx787
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dx787 8/1/2017 7:35pm
8/1/2017 7:35pm


dx787
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dx787 8/1/2017 7:36pm
8/1/2017 7:36pm Edited Date/Time 8/1/2017 7:38pm


where the screwdriver tip is where the o ring keeps blowing. it looks like the groove gets wider there and the sleeve isnt tight with jug.
dx787
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dx787 8/1/2017 7:41pm
8/1/2017 7:41pm


bottom left - look how much space is between o ring and groove
JWACK
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JWACK 8/1/2017 8:33pm
8/1/2017 8:33pm
To me it looks like they re sleeved that cylinder and didn't do a good job pressing the new one in. . I would junk it and buy a good used cylinder, one that hasn't been sleeved. Or a new one.
Paw Paw
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Paw Paw 8/1/2017 8:38pm
8/1/2017 8:38pm
JWACK wrote:
To me it looks like they re sleeved that cylinder and didn't do a good job pressing the new one in. . I would junk it...
To me it looks like they re sleeved that cylinder and didn't do a good job pressing the new one in. . I would junk it and buy a good used cylinder, one that hasn't been sleeved. Or a new one.
x2

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imoto34
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imoto34 8/1/2017 9:00pm
8/1/2017 9:00pm
Two Paw Paw's in this thread.
speed_racer
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speed_racer 8/4/2017 8:54am
8/4/2017 8:54am
The sleeve is jacked, throw that cylinder away.
NEVER sleeve a chrome plated cylinder. ( we all love Mill Tech)
You can try to surface the cylinder, but really dude you do not want 1970 technology in the newer bike.
The reason we went to a paper thin chrome plating is because an aluminum only cylinder heats and grows the same as an aluminum piston, so we can have tighter tolerances.
In all my experiences with chrome cylinders that get sleeved you will always be chasing seizure issues.
Yes, spend the $500.00 and re-do the whole top end, or you will pay with doing the top and bottom later on.
And if a shop did that fix they didn't work with me, I would've called you and made you buy a new cylinder.

I will never use a sleeve unless there is no other choice. In your situation there are cylinders available, spend the money.
The sleeve looks as though it was super hot, the surface is cooked. The big rod bearing needs to be looked at now!
I'll bet the bottom part of the sleeve doesn't match the cylinder good? Sleeve installs are tricky, you get one shot to heat the cylinder super hot and slide the sleeve in, if it's wrong you're stuck with it. They either went to deep or not deep enough with the sleeve in regards to the oring groove on the inside.

Sorry bro.

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